A resin-made fuel tank for automobile includes a fuel tank as prepared by integral molding by blow molding and a fuel tank as prepared by welding split molded bodies which are half-split by injection molding each other in a welding portion. In any case, it is necessary to make fuel barrier resistance consistent with impact resistance.    (1) In a fuel tank as prepared by integral molding by blow molding, by using a parison of plural layers, it is possible to realize a structure of plural layers with ease. Accordingly, in Japanese laid-open patent publication numbers Hei6-340033 and Hei6-191296, there is studied a multilayered structure composed of a laminate of a base layer made of a high density polyethylene (HDPE) resin which is excellent in impact resistance but poor in fuel barrier properties and a barrier layer made of an ethylene-vinyl alcohol (EVOH) copolymer resin which is excellent in fuel barrier properties. However, fuel tanks as prepared by blow molding involved such problems that the productivity is inferior to that by injection molding; that the degree of freedom of shape is limited; and that in special sites such as a pinch portion where terminal ends are pinched and flattened by blow molding and fitting hole portions to be processed for fitting parts such as valves, the barrier layer becomes discontinuous so that permeation of a fuel is increased as compared with that in general sites.    (2) On the other hand, fuel tanks as prepared by welding split molded bodies which are half-split by injection molding each other in a welding portion have such advantages that the productivity is excellent as compared with that by blow molding and that even in special sites, permeation of a fuel does not so differ from that in general sites. However, according to the injection molding, since it is difficult to realize a structure of plural layers, it is important to employ an injection molding material having excellent fuel barrier properties and impact resistance in a single layer. Up to date, in Japanese Utility Model Application number 61-89188 (JP-UM-A-62-20922), nylon 6 and nylon 12 have been mainly studied as an injection molding material. However, there was encountered such a problem that permeation of a fuel containing an alcohol such as methanol and ethanol is large. In recent years, there is also studied, in Japanese laid-open patent publication number 2002-226707, a blend of a polyphenylene sulfide (PPS) resin which is excellent in fuel barrier properties but poor in impact resistance and an olefinic resin capable of increasing impact resistance. However, there was encountered such a problem that fluidity in injection molding is insufficient.
Furthermore, in the blend of a PPS resin and an olefinic polymer, on a long-term basis, as shown by a change from a solid line to a two-dotted line in FIG. 6, there is some possibility that a fuel is stored in an olefinic polymer 52 in a PPS resin 51 and swollen, thereby causing a dimensional change. This is because it is general that the olefinic polymer is dissolved in or swollen by a fuel due to its poor fuel oil resistance.